Final answer:
The likelihood that an incumbent is defeated can be increased by campaign funding, scandals, and redistricting, but not by national political tidal waves. Incumbency advantage comes from factors like name recognition and prior election successes, while campaign funding is essential for candidate visibility and viability.
Step-by-step explanation:
The factors that may increase the likelihood that an incumbent is defeated, except for national political tidal waves, are campaign funding, scandals, and redistricting. Incumbency advantage is a phenomenon in Congressional and local elections where incumbents often win reelection due to reasons like name recognition, voting records, successful prior elections, and support from political action committees and interest groups. However, campaign funding is also critical, as it can influence the success of a candidate in elections.A phenomenon that can tilt the scales against incumbents is the coattail effect during presidential election years, or the reverse-coattail effect in midterm elections, potentially affecting their reelection prospects. Analyzing the effects of incumbency and campaign financing in House and Senate races also includes understanding how these races can be nationalized, especially during electoral years where the coattail effect comes into play.